Federal law and regulation specify the general eligibility and coverage requirements for mandatory and optional Medicaid home and community services. States use additional criteria to specify who, within the general eligibility group, will receive services. States use a number of different terms to describe these criteria: medical necessity criteria, health and functional criteria, level-of-care criteria, and service criteria. These terms are often used interchangeably, but, in fact, may have specific meanings in state usage, which may differ from usage in Federal requirements. When referring to any of these criteria, this Primer uses the term service criteria. The degree of flexibility states have in setting these criteria depends on whether the service is Federally mandated or a state option and, if optional, whether it is offered under the State Plan or through a waiver program.